Field of the Invention
The invention pertains to a control arrangement for a transport refrigeration system that has heating and cooling capabilities and a refrigerant compressor driven by an internal combustion engine having multiple speed capabilities.
My U.S. Pat. No. 4,325,224 describes and claims a transport refrigeration system control arrangement in which an electronic thermostat of the type available from the assignee of this application under the trademark "THERMO GUARD", is used in a control arrangement along with an auxiliary control relay and time delay means. The arrangement functions to keep the compressor operating at a lower speed for longer periods of time when the temperature in the served space is in the relatively close range of temperatures above and below a setpoint temperature. It overrides a call for operation of the compressor at a higher speed when the sensed, temperature in the space moves either above or below the relatively close range until at least a predetermined period of time has elapsed with an uninterrupted call for higher speed operation existing, and then the compressor operates at the higher speed. This arrangement, which is in commercial use, provides significant fuel economies in connection with a continuously operating internal combustion engine.
It is also known to provide transport refrigeration systems with an internal combustion engine driving the refrigerant compressor with a control arrangement which provides for automatic starting and stopping of the engine in accordance with temperature requirements of the served space.
U.S. Pat. No. 2,850,001 is a relatively old patent which speaks of a start-stop arrangement in connection with the type of transport refrigeration system then in use.
U.S. Pat. No. 3,926,167 states among its objects the provision of an automatic starting device for a diesel engine as well as to provide a control for a diesel refrigeration unit such that the engine will be started when the thermostat calls for cooling or heating, and then the engine will be turned off when the temperature requirement has been satisfied, to the end of minimizing running time of the engine and reducing use of engine fuel. The arrangement in this patent is such that a typical transport refrigeration control system is modified so that any low speed operation of the engine is eliminated and the system works on a start-stop cycle at high speed whether heating or cooling. The control arrangement does not provide for any optional continuous engine running cycle.
It is the overall aim of my invention to provide a control arrangement for a transport refrigeration system in which the user may elect to run the system in a continuous cycling mode or optionally may elect to operate it in a start-stop mode in which the engine operation is terminated when the served spaced temperature is in a range near setpoint. Additionally, the control arrangement is intended to be such that the operation of the engine at low speed is for all practical purposes maximized, and is available irrespective of whether the system is operating in a continuous mode or a start-stop mode.
In addition to the attainment of the foregoing objects, another object is to provide for a shutdown arrangement under starting malfunction conditions which shuts down all of the system except for that required to indicate a malfunction.